These deaths have been linked to Australia’s unusually hot summer. Despite flying foxes being well-adapted to Australia’s climate, they are incapable of regulating their body temperature in extreme weather and resultantly die from overheating. In January, Sydney’s temperatures reached 47oc, its highest since 1939, killing hundreds of flying foxes. This, however, pales in comparison to southeast Queensland’s 2014 scorching heats, when 45,000 flying foxes died in just one day, with some colonies more than half wiped out.
These phenomena are defined as mass mortality events (MME), catastrophic incidents which simultaneously kill vast quantities of a single species in a short amount of time. Evidence shows that between 1940 and 2012 these events have not only become increasingly frequent for birds, fish and marine invertebrates, but also kill a larger number of animals in each event. With 727 reported MMEs occurring since 1940, this poses an immense threat to global ecosystems as MMEs have the potential to put an entire species at risk.
MMEs are often triggered by an interplay of stressors. Diseases and highly transmissible infections are the most frequent causes, influencing 25% of MMEs. A further quarter of MMEs are attributed to climatic and environmental factors, including temperature extremes and oxygen stress. Further stressors include starvation and the introduction of alien species.
Of most concern to scientists, however, is the increasing role human activity plays in MMEs. As pollution accelerates global warming and increases extreme weather incidents, high magnitude MMEs will become more frequent. This is particularly disturbing as mammals take hundreds of years to adapt to climatic changes, making elk and reindeer especially vulnerable to MMEs.
This is particularly exemplified by the May 2015 saiga antelope MME. When the migratory animals aggregated for their annual calving in Kazakhstan’s Betpak-Dala Desert, they rapidly began dropping dead. This occurred on an immense scale; 200,000 antelope died in merely three weeks, which represented 80% of central Kazakhstan’s population and 62% of the global population of this critically-endangered species. Researchers were baffled by this seemingly inexplicable event, which caught global media attention and attracted considerable and divergent speculation, until pasteurella multocida was discovered in the bloodstream of dead antelope. This bacteria is usually prevalent in their tonsils without consequences, but unusually high humidity and temperatures of 37oc spread it into their bloodstream, causing hemorrhagic septicaemia. While low-lying pasteurella multocida exists naturally, it was undoubtedly aggravated by anthropogenic climatic stressors.
Mankind’s influence on MMEs is further illustrated by a mysterious outbreak along America’s west coast in 2013 in which hundreds of millions of starfish seemingly “melted” into white gunk. Higher temperatures and warmer seas in 2013 spread parvovirus and resultant gastrointestinal problems among 20 starfish species. This increased their vulnerability to bacterial infections including the sea star wasting disease. Cuts rapidly developed in the starfish’s infected arms, which some ripped off before quickly becoming lifeless. Similar to the saiga crisis, the MME was caused by a naturally-occurring virus, ultimately exacerbated by climate change.
When will mankind cease causing such large-scale destruction?
With conclusive evidence illustrating climate change’s detriment to ecosystems around the globe, it is imperative that Trump stops being in denial so that fauna such as flying foxes, saiga antelope and starfish are ultimately saved from extinction.
